I'm not sure about VF-1 vs. X-wing, unless you're in atmosphere. VF-1 pulls, what, 10 Gs? In space, the X-wing does 3,700 (according to EGVV) The X-Wing has shields, which the Valk doesn't, and presumably heavier lasers. Plus the X-wing has acceleration compensators, which would allow it to pull more Gs in a turn than the Valk can. Best chance a (FAST-Pack equipped) Valk would have against an X-wing would be to let it get in behind him, then pop off a couple of aft-facing SRMs.
That would be a tough fight. As I understand it, all Gundams generate Minovsky particles, which blind both IR and Radar detection, leaving it a visual fight, and rendering most missile systems useless (and I don't think Valks carry laser-guided). Just what type of Gundam are we talking about here?