In most cases, I would say yes - you'll get more performance from a pure tube amp. Tube integrated amps often have very simplistic preamp & volume stages in order to fit into the same box & budget. Simplistic is fine, but...if you hear an ARC Reference 6 or VAC Master, you will know what a big box pre can do (neither of these will come close to fitting into an integrated). The power amp section of an integrated could also be compromised a little for those reasons. Having to use an extra set of interconnects sucks, but still worth it imo.
The biggest stopper to most people going to separates is having to buy 2 components up front instead of one - but you've already got the preamp. Go for the tube power! You'll also gain more flexibility down the road - sometimes the brand-matching pre & power aren't actually the best sonic match in your system, to your ears.