it makes no difference what weight or hight you are, iv seen 15-16 stone blokes ride a mod better than most and iv seen scrawny weedy 5 foot blokes throw around a long stock bike, you have to get the bike YOU like the most
by the time you are good enough to know whether you made the right choice or not (and beleve me the only way to know is to actualy ride the bike) you will prob be thinking of upgrading anyway so go with your gut feeling - watch some trials vids what style of riding suits you? who do you look up to etc..
the stock vs mod debate will always be found on trials forums untill the sport is dead and gone and as i said there is no answer its up to you.
what you usualy get as an answer is sombodys persoanl preference in bikes - this is not good enough justification for spending £400 plus, however ase there is no answer here is my opinion
i find stock bikes more hastle than mods, gears and derailers and gear shifters etc.. plus they are alot bigger so if you aint got much room in your garage/flat/house/bedroom then they can be a pain in the ar5. stock bikes are also more expensive in every way ie. a good stock hub is £100-£350 where as a good mod hub is £40 plus a £12 acs claw for the same performance (almost). stock bikes are roumoured to hop higher as you are already an extra 6" of the ground, i have never seen this proved. stock bikes do make you go bigger eventualy as they are bigger themselves and the geometry on good stock frames like a zoo pitbull or onza t-rex is geard towards this. stock bikes are more stable than mods, mods have twitchier steering as they have smaller wheels. mod bikes do make you learn alittle faster (depending on how comited you are) as they are eaisy to throw around so make those first few confidence inspiring hops alittle easier. mods usualy use an ACS claw freewheel or better these have 36 engagement points, that is singly the best thing you could ask for on a trials bike.
and finaly - i think the t-pro rules the world - exactly the same geometry as a koxx level boss, which costs way over double the price. plus its a great speck and looks sexy - in comparison the t-rex is a medioca spec with nice geometry and good potential for upgrade / progresion altho for tha cash my moneys on the T-pro all the way
sorry that was abit long - like i said get the one YOU like the most, from there on its all good :) trust