I prepared a test-bench for you in Cadence ADE by using Spectre simulator.If you abel to access to this simulator, you can do the same thing to find the FTmax.
As you see, FT has a max. value where the Collector/Base current is optimal.You can use this function to find the max. FT.
This is FT. vs Ibase ( of course Icoll) curve of BFP420 of Infineon and it has exactly FTmax ( 25GHz) as mentioned in its datasheet
Code:
unityGainFreq(mag((IF("/Q0/C") / IF("/Q0/B"))))]
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