Mirage IV with Spey engines.

[si-h]

Just doing a bit of late night reading......
Apparently, the French offered a Spey engined Mirage IV bomber, after the TSR-2 was binned.
The Mirage IV was a fast thing, M2.2.
The Speys would have given an extra 10,000lb's of thrust.
We are told Speys are bigger, more drag etc.....
Would this have made a massive increase in speed ?
Can anybody calculate/guestimate this ? No good reason.. just thinking ! Cheers !