Hi Bill Albrant,
the MSP430FR5739 can run at up to 24MHz! Yes, it is a 3.6V (max) device, but where's the problem? When you need to connect it to 5V peripherals you can use level shifters i.e. like the TXS0104E (4-bit OD) or SN74CB3T1G125 (1-bit); find…