the clausius-clayperon equation contains the perfect gas assumption, which is normally valid below 5bars. Personally, I prefer a more real answer, so I would look up the steam table (ie. Thermodynamic and Transport Properrties of Fluids by GFC Rogers & YR Mayhew)
P1 = 85bar, Ts1 = 299.2C
P2 = 90bar, Ts2 = 303.3C
(Ts: Saturated Temperature)
a more real value for the required pressure can be extracted by interpolation of the above data:
P = P1 + (300-299.2)/(303.3-299.2) x (P2 - P1) = 85.97 ~ 86bar
I wouldn't treat steam as a perfect gas because water is polar molecule that exhibits hydrogen bonding. moreover, the required pressure to condense steam at 300K is clearly above 5bars.