The 900 Monster's extra kilos do give it a slightly more reassuring feel, and paying the price of marginally reduced agility is more than made up for by this.
But the big gains, in not just speed but enjoyment, come from the extra power of the motor. An 80% boost in power is, unsurprisingly, easy to detect as soon as the throttle is twisted. There's just so much more stomp and response from the motor, you could never go back to a 600.
Route planning is nowhere near as essential on the 900 as it is on the smaller Monster. The extra speed means it's 'competitive' on all sorts of roads, and makes for quite a good all-rounder. Don't think for a minute it's a racer that can take on focused sporting tackle, because it's not quite fast enough for that. But it is rapid enough to give thrills, and if you want to lose your wheelie virginity, the 900 Monster is the business.
Life at continual high speed gets a bit unpleasant without a fairing as it does to a slightly lesser extent on the 600. And like that version, pillion provision hasn't been on the top of the designer's agenda. Passengers will survive OK for a while, but the slim seat doesn't give enough support for longer rides.
Practicality didn't get too much consideration either. There are a couple of grabrails for the pillion, but they're better used as bungee loops. There's no centrestand and the instrumentation is basic and doesn't feature a clock. Underseat storage can't accommodate much more than a credit card. If you want to carry any odd and sods on a Monster, then wear a jacket with deep pockets or a backpack.
Choosing which Monster suits you best is very much down to your need for speed and how important having a bike with an appreciably greater amount of grunt is to you. It does, after all, affect every aspect of your riding experience.
The 600 is best described as a stylish tool for getting you around from A to B at a modest pace. It's not designed to go very fast, and rarely provides enough gusto to stir the loins even when you cane it within an inch of its life. The lack of performance from its little motor ultimately restricts its use and thrill power.
But if you're not in a rush and want something that's dead easy to ride, especially in town, and won't scare the pants off you every time you open the throttle, then the cheapest version of the Monster is the right one for you. It has to be said it's a ladies' favourite too, with its less intimidating attitude, yet it's still a macho-looking bike. If you're into the pose, the Monster Dark is cheap money for the kudos the badge of Ducati carries, not unlike Harley-Davidson's entry-level 883 Sportster which sells for under £5,000, priced low to get you hooked into the brand. You see a lot of Monster 600s around the streets of London for that reason - the right image at the right price.
However if you need a little more from a bike, then the 900 has to be considered. Its extra speed makes it more of an all-rounder. It's something you can consider for the sort of lengthy journeys the 600 would struggle with but what it really comes down to is something entirely personal. If you're a more aggressive rider, the bigger Monster is simply a damned sight more fun.
Depending on exactly which model you opt for will dictate the exact price differential over the 600. The glitterball Metallic version we tested is another £300 more than the Monster 900 Dark. So like-for-like, look at spending another £2,000 for the privilege of the extra power. On top of that, running costs like servicing, tyres and insurance are all higher and add to the overall costs of 900 ownership. Sounds like a lot? Well have a go on each and decide - you might find it's a price worth paying.
Technically the 600 and 900 Monsters are very closely related, featuring simple but effective engine and chassis engineering.
As far as engine designs go, the 90¡ V-twin Monsters are very dated. Air-cooled, with only two valves per cylinder, it's no wonder the power and performance of the low-revving motors is only modest.
But one technically interesting feature of the Monster motors, and something unique to all Ducati engines, is the Desmo valve gear arrangement. The near fifty year-old design is not new. But the use of camshafts to both open and close the valves, therefore eliminating springs, is certainly different.
One concession to the modern era is the 900's fuel-injection system. It provides cleaner and crisper fuelling via its 45mm throttle bodies than the 600's 38mm carbs. The extra and more broadly spread power of the 900 means it can use a five speed gearbox. The 600 has an extra ratio. The bigger bike has an oil cooler as standard to keep its engine temperature consistent.
Chassis format of the Monsters is very similar. The steel tube trellis frame might not look up to much, but it's easily strong and light enough - it's the same design used on all of Ducati's WSB championship-winning superbikes. Suspension is exactly the same on each bike. The 43mm upside down forks are non-adjustable and the rising-rate monoshocks can only be altered for pre-load and rebound damping. The bigger Monster features twin-disc front brakes, the 600 only has one. But otherwise the rest of the rolling chassis, bodywork, and cycle parts are virtually identical. That's £2,300 for a bigger engine, fuel-injection and an extra disc. Looking at it that way, it's a harder one to call.