You can NOT make generalizations about the difference between Aluminum and stainless props.
1. Stainless props of the SAME design (rake, blade area, cupping etc.), manufacturer and size (diameter and pitch) as the aluminum they replace WILL run about 200 RPM faster. Because of less flex and less drag through the water they will also increase speed slightly.
2 because of different blade area, cupping, rake, etc. stainless props of different design and manufacturer than the aluminum can either turn faster or slower than the original aluminum they are replacing.
3. Best bet is to repost in the prop section and wait for someone with experience in that particular swap to amswer