A scenario where the Republicans in 1994 performed even better than they did in OTL, perhaps near 300 house seats and 60 senate seats. Would this happen under Clinton? Or would this be more likely under Dukakis in '88, Cuomo, Brown, etc. in '92?
The only losing Republican Senate candidates who came within nine points of winning were Michael Huffington in CA, Charles Haytayan in NJ, Colin R. McMilan in NM, and Oliver North in VA. https://en.wikipedia.org/wiki/United_States_Senate_elections,_1994 Even if all four won (and having someone like McMilan who lost by almost eight points winning is a stretch) it would only make for a 56-44 Senate, though it would be 58-42 after Richard Shelby and Ben Nighthorse Campbell changed parties. But really there is no particular reason to expect the Republicans to do better than they did; indeed, given that the economy had improved in 1993-4 (by November 1994 unemployment was down to 5.6 percent compared to the 7.4 percent it was when Clinton was elected https://fred.stlouisfed.org/data/UNRATE.txt ) they were lucky to have won as many seats as they did.