What a tour...this is really a great and also challenging tour. I like to climb up and I'm not too good in technical downhill trail biking. So there were some places where I had to push the bike.
I did it in 3 days.
First day from Fiesch to Mörel: After a long but not too steep and not technical climb the first check point Märjela is reached. Here you have to walk down to the glacier and enjoy the amazing view. Only do the turn from Märjela to Fiescheralp if you are able to bike an S3. It has a lot of stones and there is no space beside the trail and a mistake could have serious consequences.
The final climb to the Moosfluh is the final climb challenge of the day, but it is worth it. The small turn on top of the Moosfluh is at least a hard S2. I had to push some parts. Also be careful on the downhill from Riederalp to Mörel, there also some parts could have serious consequences on a crash.
Day 2 from Mörel to Ernen: The challenge on this part is the climb to the Breithorn. As soon as you enter the old forest street you start to smile, if the ascent is less than 12%. For the next 8-9km the ascent is between 12 and 17%...technical not difficult, but you will feel the 2000 high meters from the first day. Afterwards it is nearly just a downhill to Binn and Ernen (just some small climbing meters). In Ernen the hotel BerglandHof is a great place to stay. Very friendly and amazing good food.
Day 3 from Ernen to Fiesch: Easiest day, but do not underestimate the last 1000 high meters. The most of them are collected on small uphill parts followed a downhill, but the last 300 high meters up to Bellwald are the last uphill challenge. The trail is cool and depending on the power in the legs there should not be a lot of pushing parts. The downhill from Bellwald to Fiesch is great. Some roots in the forest are tricky and require to stay concentrated.