I seem to have my FS going reasonably well around Leominster don't I?
As for the wheels I have run a ZX5 for about 3 years now and this weekend will be the first ever time it has run with Kyosho wheels on both ends of the car!!!! Wheel fitment (Losi fitting I assume you mean) is more than possible, not desirable with the later ZX5FS2 / RB5SP2 rear ends though but with an FS it's simple enough.
As for strength I rarely break anything, if I do it's usually a "car coming the other way" sort of accident and is normally just a front shock tower, worst case a shock shaft. The tower issue will be sorted in a couple of weeks time when we have the Desire RcRacing towers for the car ... break them, I dare you to try
Dont' write the ZX5 off just yet and if you want a drive of mine to help decide if you like it (sure you will) just ask ... about time I came back to Hereford now I've found (I think) the cause of my interference there!