Basically, the two steering wheels are functionally the same or very, very similar, even the driver is the same. The steering wheel is the same size and has only slightly different key layout (the PS4 Share button is added at T300RS, for PC games without significance). There is a crucial difference, however, in the shift paddles, the T300RS this has on the steering wheel (ie rotate with) and the T500RS has fixed paddles - what is better is a matter of taste.
When Force Feedback (FFB) is the T300RS no way inferior, if perhaps a tiny reserve is also the T500RS yet upwards. But could the T300RS compared possibly attest a slightly higher Drehwilligkeit (smooth), but it really falls on only in direct comparison and is, in my view, a matter of taste.
The pedals of T500RS are of course in a different league, especially since there is no coupling at T300RS - for me the lack of coupling is more of a plus because so I can pedals symmetrical to "Playseat" assembled and get much better Ran.
Oh yes, the fan and the noise associated: When T500RS this is a hotly debated topic, but when T300RS this discussion should fall silent, so far I have not heard a fan.
The steering wheel housing of T300RS is quite a bit smaller and lighter compared to T500RS.
The T300RS has an integrated power supply and it thus needs no external power supply more, just as it is when T500RS. Also the connector is only one Europe instead of IEC connector, so to put more compact and easier if the power strip already overflowing.
The price is of course ne number, but so as to obtain a Lenkradset which has far exceeded the level of a toy and is completely dedicated to the race and beat their best times, instead of having to deal with shortcomings / compromises.
All in all, the T300RS an absolutely recommendable Lenkradset which is the T500RS just worthy to the pedals.
Postscript
========
After I completed some longer sessions with the steering wheel, I am more and more impressed by the T300RS. However, quite silently, the steering wheel is not, fortunately, far less noticeable than when T500RS and accordingly only (?!) To hear during breaks.