What about the Yaesu FT-2980E:
It is theoretically small and light enough for SOTA. Yaesu advertise it as having an excellent large signal handling capability due to the design with a special front end filter. It is also cheaper and many times more powerful than a lot of HTs. If I did nothing but FM for SOTA, I would be tempted to buy one.
73 de TF/OE6FEG/P
Matt