I'd definitely recommend going with the 9500Pro over waiting for Trident's XP4.
I really don't expect the XP4 to perform substantially better then the 9000Pro board, let alone the 9500Pro.
Keep in mind even the fastest Trident XP in the XP4 has an MSRP of only $99.
I'd be expecting Ti4200 performance at best, and likely a bit off that.
Most of Trident's claims fall roughly in-line with Ti4200 performance levels.
The 9500Pro will almost assuredly be faster and give you full DX9 hardware support, which the XP4 lacks.
This is only referring strictly to 3D performance... when we consider areas like DVD and TV-Out, the hallmark of ATi's reputation then I find it increasingly clear the 9500Pro is a much much better option.
But then, this is to be expected. The XP4 is intended to compete against the fastest of the R9000/GF4 MX lines, rsopectively that would be the R9000Pro and GF4 MX460.