New bike for the spring: what size???

1) your physical size (both height and weight are important)
5 foot 4 - 140lbs
2) How physical / aggressive are you ?
Too agressive
3) what do you plan to ride- MX/SX tracks, woods, fields with friends or ?????
Outdoor MX
4) Do you have any riding experience?
10+ years
5) Do you think you will race ?
For sure
6) Are you mechanically inclined and will you be doing your own bike work?
Depending on what's wrong (I can handle doing a top end on a two-stroke)
7) Do YOU have a preferance to a brand/ motor choice (2 or 4 stroke)?
More experience on a two-stroke but not opposed to a 4-stroke
8) Do you have a dealer close by your home that you might use and what brand(s) does he carry?
Yes - he carries GasGas, TM (not KTM), Kawasaki
9) How much ($) do you plan to spend on a bike?
$4000 ish
10) Do you live in California?
Noooo Canada
11) Your age?
19
12) anything else that you think would help form an opinion

Well, I raced in the 125 class all through highschool. The summer after graduating I broke my arm and couldn't race for 8 weeks (got a nice steel plate in there etc.) I went off to University, sold my 125 and got a kx250 that I built for the trails... now that I have a year off school I've been beating the crap out of my 250 two stroke in the pit and plan on racing in the spring - my question is... what size of bike???
I love the 250 two-stroke's power, it's savage with me on it and I can make jumps I never dreamed of on the 125, however it really beats me up in the rough/tight stuff. A lot of tracks here are tight and I don't know if I will be able to be consistent on such a big bike. 125's aren't as exciting, but I have a line on a really nice 2006 rm125 that i could send down south to be converted to a 144... or there's the question... maybe a 250f? I figure everyone else here races 4-strokes maybe there's somethin' to it? :P
Thanks in advance,

PS - here in Canada 150cc and under two strokes race with 250f's (mx2), 285cc and under two strokes race with 450fs (mx1)... and then we have an Open class (GP) that's open to bikes under 650cc... I plan on racing either mx1 and GP or mx2 and GP depending on what bike I get.

come on guys.. no input?
I'm very much leaning towards an rm125 or cr125 which I will get 144-ized.

I'll be in the Junior class; i was a top 5 junior up until i stopped racing. Most of my competition has moved up to intermediate so hopefully there isn't too many nutjob younguns that have moved up from 80's :P
The kx already has a 10oz. flywheel weight, porting, a 120 rear tire, and suspension sprung for me... it's just really top heavy and fat feeling compared to the newer 125's that i'm used to... it's kind of like a dumptruck in comparison.
In contrast to our field of around 30 bikes in the 125 class, our 250 class is tiny and doesn't even have enough riders for upgrade points to be awarded. Since I don't want to be in junior forever, that option is out. I can ride the 250 in GP, so I might keep it for that. That leaves the 125 class, which I'll probably get a 144 for - I've got two reasons: 1) Don't want to hop between a four-stroke and a two stroke for different classes - I'm afraid a 250f will promote a "lazy" (lower rpm) riding style that will adversly affect the way I ride my 250 two stroke. Despite the flywheel weight, which helps it hook up A LOT better, it still makes much more roost in the upper rpms.
2) Cost - I'll be able to get a 125, get it 144'd and put a pipe on it for around the same price as a solid 250f, plus I'll know the engine is good.

Thanks for the input