Get the M03L plus buy a spare body that will fit the M03 length chassis, either the M03 minicooper body, or if you want something different, the Honda s800 body also fits the M03 (but not the MO3L) (discontinued, I have a couple left if anyone is interested, PM me).

I have raced all three (M04M, M03, M03L) on carpet on a regular basis. I used the M03L to win the TCS Nationals in 2003. My take on the comparison is this.

The M03 can be the faster car overall of the front-drivers. It is amazing, but the M03, with its slightly shorter chassis (due to removal or lack of the 20mm chassis extension piece (with its four screws) and the slightly smaller body, is a couple of ounces lighter than an M03L. I didn't think it was that much until I put each car on a scale. Now a couple of ounces may not seem like much, but the extra punch out of a corner is noticeable. If we were running something other than silver cans it might be different, but with power always at a premium, those couple ounces make a difference.

While the M03 can be a touch faster, it is also a bit more twitchy. The M03L is definitely easier to drive on most layouts. If you can handle the M03's twitchiness, that can be the faster car. All things considered, I generally like the M03L over the M03 (except when I racing Eric Whippler (TCS 2001 Nationals champ), who always uses the M03, where the weight difference is so noticeable (acceleration out of the corner) it makes my M03L look like it has thrown an anchor out back!)

You didn't mention the M04M chassis (rear drive, with the smaller 60D tires just like the M03). Too bad it is gear limited in TCS (19T vs 20T pinion) that can't be legally matched up for pinion size. (That one tooth difference is a REAL killer on the Tamiya CA track, with the 125' straight plus sweeper. So much time is spent on that track at max RPM that the M03's waive goodbye to the M04's). The M04M can kill the M03's with superior roll speed on the right track layouts - not all the commotion going on up front like the M03 front drivers, and a lower center of gravity not having the servo up on top of the chassis. I had my 13 year old son driving the M03L and not an M04M because I felt the M04M was harder to drive (but potentially faster than both M03 and M03L if you have the same size pinion (not TCS legal) in them). There are times that you have to be gentle on the throttle of the M04's on carpet (from a dead stop) or the back end can break way on you. He then asked to try my M04M, and he's been hooked ever since, qualifying for the top half of the A at our TCS regional. Just seems to suit his driving style, and who am I to argue!