Thanks to all who put in time and effort about the RS4 and the RS6. I want to replace my Fanatic Blast with the RS4 and my bigger boards with the RS6.
I'm 63 and live inland (Lancaster County, Pennsylvania USA) and mostly use an 8.5 though I'm 125 lbs. and 5' 2". Sorry, I don't know the metric equivalent.
For years, I only had one board: a 2002 Exocet Speed Slider. It worked for me from 4.5 to 8.5. Then I got into a board buying binge.
The Speed Slider worked great but I wanted something that planed a little earlier and maybe try the new style of shorter boards (although I used to have a Starboard Hypersonic 105 that planed extremely early and had the same wind range) I got rid of that because it did not scholg well. Unless I travel 2 1/2 + hours to the shore, most of my time is spent schlogging. The Speed Slider schlogged for me almost like a longboard.
So I called Extreme Windsurfing in Lakes Bay, NJ and asked if he had any good deals on boards. I bought a freight damaged Blast 115 for only about 1k. It was OK at first but it is not an early planer and it did not schlog the greatest. It reminded me of the Hypersonic. I wanted to sell then not sell then sell etc. but now I will sell it again on ebay.
Then I found someone from Greece who was selling a 2015 RS4. Judging from all of the adds and comments, it seems it would be a great board for me. It should be arriving in a few days. It turns out that he also has a 2013 RS6 so I am going to get that also for the extreme light wind days under or around 12 knots.
So I am excited to try out the new boards hoping that they will satisfy most of the weather we get locally.

It sounds like volume is your problem not which board/brand to buy.

There's a Facebook USA windsurfing classified group that is great for buying second hand gear. Probably cheaper than shipping a board in from Greece.

Last time I visited Sandy Point in Daytona Beach (the USA importer for Exocet) they had a 2nd hand RS6 in pristine condition. I can't remember the price, but they usually sell the second hand gear for very reasonable prices. Call them, they don't put the decent second hand gear on their website, I think it's to favor the local buyers.

You will love the RS4 I have the same board and it is fast, comfortable and so easy to gybe

You might be better off with a long board like an old Mistral One Design. They go very nicely in non-planing conditions.

Thanks for the advice guys. I've had the RS4 for one season here in central Pennsylvania USA and I absolutely love it! It is so much better than the Blast for me. I've been using the 8.5 with no problem. When the wind is really light though, it doesn't schlog comfortably so I will be getting the RS 6 delivered very soon. Ideally, the RS 5 would have been my best bet but beggars can't be choosers. The great deals I got overseas beat the Sandy Point prices by many hundred dollars even with shipping. When I checked the site most all of the RS boards were out of stock anyway.