Don't be too miffed about not getting Splatterhouse to run full speed... it's a tricky and taxing arcade game to emulate.
Most arcade games of the time had 2 CPUs - Spatterhouse has a whopping 4x CPUs... and it's not a simple CPU to emulate. There are 3x M6809 and a M6808 (like a 6809) which are the more taxing 8-bit CPUs to emulate.
Do you have a Dingoo A320? It does a pretty good job of getting 100% speed but does have some frameskip.