I know both RSM and Hawthorns well.
RSM is linked to a Reigate Grammar and most but not all get the green light to proceed to the Grammar without exam. It’s not so nice a yr5 and 6 for those who don’t get the green light or who choose to go elsewhere. But if your kids are academic and that’s the senior you definitely want it can be a good choice because 11+ is stressful. It doesn’t have the traditional Prep feel of Hawthorns, partly because it doesn’t have the Yr 7 and 8s. They don’t do Latin or as many languages and it is more of a town based school. Although some drive in from outside Reigate/Redhill and the v close villages, it’s more locally based than Hawthorns. Lots seem to walk in, which is good as the traffic to get there and parking is bad. Lots of people choose it for the through to the Grammar thing. It’s had lots of investment in the last 15 years and gets to use some grammar facilities such as the pool or sports ground down in Woodhatch.
Hawthorns as you know is in an amazing setting. There is good use of the woods and grounds in the learning and it seems to keep children young, perhaps because it’s a bit cut off. The main secondaries they feed into are Caterham, Dunnottar, Reigate Grammar but they also send to the 13+ public schools for boarding and schools like Whitgift, woldingham, Ardingly, Sevenoaks, Hurst. Some of these are very academic and some less so. I think many Hawthorns parents are not dead set on a certain Senior school at entry but like the fact kids go to lots of places and choices can be gradually made. So Hawthorns do prep for a range of entrance exams but early yr 6 is quite a stressful time for families, although some later say their kids gained from having to go through process. There’s a lot of specialist teaching from Yr3 including seceral languages as they go up school. Existence of Yr 7 and 8 make it feel different to a primary or prep that goes to 11. I think fees are RSM and Hawthorns are similar. Hawthorns probably draws from a wider geographical area to include Reigate, Horley area, Caterham, Oxted, up to Walton and Kingswood and down to Crawley plus all the villages. Lots of parents went to traditional Preps or boarding schools and perhaps trust the school to advise about appropriate secondaries and can see value in different types of schools for different kids - siblings often seem to go onto different seniors
There’s also Micklefield in Reigate which sends about half to the Grammar and half to Dunnottar, plus a few around the Caterham area like Oakhyrst Grange.
I’d imagine both are offering virtual tours and could put you in touch with current parents for a chat. Hard to choose when you can’t visit. Both are good and seem to produce confident kids who are well prepared for the next stage, so you can’t really go wrong with either.