I am really tempted to go for the Infinity's but any suggestions are welcome:
No.

Infinity RS152 Review (Surround Speaker)
This is a quick review and raw measurements of the Infinity RS152 surround speaker. It was kindly purchased new (last year!) and sent to me directly for testing. They current costs US $449 for a pair but Harman is know to have blow out discounts on these speakers at times. Edit: our company...

Can can your current speakers be moved down just to check the theory?
A rough layout of the room with speaker locations might be helpful.
Could the existing speakers be used as rear top or rear height in your atmos setup with or without using surround back speakers?