Should I change my Pump Impeller or buy a Variable Speed Pump?

[Dead Beaver Ranch]

Here's my setup:
~20,000 Gal Inground pool with Vinyl liner
Sand filter Hayward S244T
Pentair Rainbow 320 Automatic Chlorine (used very rarely)
Hayward booster pump for Polaris 280 pressure side cleaner
Hayward Heatpro Heatpump
All pipe is 1.5"

As best I can tell the pump is a Hayward Pump Model #SP2607X10. I can't be certain as the label is missing and the motor is not the original motor. The current motor is an A.O. Smith 1.0 HP/1.0 SF. I calculate I have less than a 20' head if I average the line coming from the skimmer and the line coming from the bottom drain. If so, the specs for the pump shows 85 GPM for a 20' head. Based on my other equipment it looks like what I really need is about 45 GPM.

If this is all correct it appears to me that I have WAY more pump than I need. I have read here that I can benefit from changing out the impeller. The pump motor is new while the pump itself is older but still has some good life left in it. I am getting sand blowing out onto the steps of the pool. I replaced all the internal components in the sand filter but this has not corrected the problem. I'm thinking the real issue is the pump is oversized. I am assuming it currently has 1 hp rated impeller (SPX2610C). I am thinking I want to change the impeller to solve my problem and save on electricity. It also looks like the impeller is the only part I would need to replace as the diffuser would stay the same. I watched very closely when the service man replaced the pump motor so I am pretty confident I can handle the task of changing the impeller.

My questions is should I replace the impeller or purchase a different (variable speed) pump?
If the recommendation is that I replace the impeller, which one should I use (SPX2607C or SPX2605C)?

Thanks for your help. This site has been very helpful to this first time pool owner.