I got rid of my 275 6 months back for an E92 M3, let me persuade you not to do the same. Mines a Monte Carlo edition with upgraded comp pack EDC (MC's have the Comp springs as well), GTS gearbox software. Some Other bits. The V8 drew me in and the E92 M3 is at a funny time of its life, I figured now would be one of my last chances to own the E92 M3 before they became dogs or got really expensive.
Based on my own experiences so far the Megane was far more of an event to drive and I often regret selling it, you'll hate the increase in weight especially given yours has been on a diet you'll really feel it, the steering is quite poor as well being hydraulic it feels slow and mushy vs that excellent electric push rod setup in the Meg. You'll also miss being able to get on the power in a corner. Its also far less usable in the winter, especially when salty. Totally different driving experience, more of an 8/10ths GT car vs the 10/10ths the Megane is. I wouldn't use an e92 m3 as a track car, too heavy and the brakes will need a £3-4k BBK upgrade as they can get a bit crappy when you really work them. Fine for road use. I also think stripping the interior, remapping the steering rack so its faster and putting it on coilovers would make a much more engaging car from it, but out the box it is literally an 8/10ths GT barge, you'd have to throw 5 grand at it to get it to a more track focused car. If you lived in Surrey Id happily take you for a drive.
Thats not the say the E92 isnt excellent, it can be driven hard and although it wont give the same confidence inspiring lateral grip the Megane does I rekon it might keep up in sweeping back roads. Its fairly quick as well, a mapped Megane would about keep up until about 90/100 where the M3 would have the legs then.
Its expensive to run as well but do your homework you'll see what they cost. Some big bills lurk with tyres and brake discs, but if youre not fussed about fbmwsh then servicing isnt really that bad. Oil and spark plugs will probably be your most expensive service cost. 170 miles to an £80 tank of premium if you drive in heavy traffic but people manage to eek 200-220 out of them on a more gentle motorway commute. So consider that as well.
Id keep the Meg.