[jws]

The difference in RISC/CISC instruction count is closer to 2:1 than 10:1. (Unless you are using a VAX polynomial evaluation opcode, but that is an extreme.)

ARM ameliorates this by having multiple instruction sets. The Thumb instructions are a denser encoding, if somewhat slower. 90/10 rules apply.

[ryanpetrich]

Thumb instructions are the same speed, but can only perform a subset of what the ARM instruction set can; each instruction takes half the space. Thumb can be faster if it eliminates cache overflows, but can also be a lot slower if faster ARM instructions have to be emulated with Thumb equivalents.