Since you're going to test buff the beginning of this wont be relevant, but I'm including for those who need it.
This has been my path for leveling single characters quickly for years. Generally this was 1 character and a J1 tank merc, which are super OP into the 50's or so. The beginning levels stay close so you can get through the first 30 levels that just fly by without running all over the place. - This path holds up well for a group of boxed chars, but the levels might need slight tweaking. I started using RG after my knowledge of the game was extensive and my ability to PL was even greater, so new groups on live generally don't experience much of the lower levels.
1-10 - Tutorial - Leave with a decent set of defiant level gear
Alternate - You can just start in CR newbie yard if you want to skip tutorial entirely.
10-18 - Crescent Reach newbie yard - Mobs get higher the further north you go until the undead. Gear drops from trash several plat each.
18-22 - Rats and Snakes in Blightfire Moors at CR zoneline/PoK Book.
22-32 - Mushrooms by the dragon corpse in Blightfire Moors - Dragoneater used to be his own placeholder and nets 50+ plat per kill with nearby vendors. He still pops pretty often. More than enough to cover spell costs for awhile. These can spawn pretty deep red at 22, so without OP tank merc, perhaps hold off a few levels before coming over here.
- Add in - 32-36 - Probably worth adding the undead in northwest of Blightfire Moors here as CoM at 32 can be rough, but again, J1 tank mercs pretty OP.
32-45 - City of Mist - Again, generally the further north you go, the higher level the mobs
?-65/71 - The Hole - You can grind in the hole for a very long time.
65-75 - Splitpaw - Mages and Druids rejoice, use those anti-summoned nukes. - 1 char 1 tank merc really slows down here.
**--This is generally the end of the 1 character and 1 tank merc section of the path - This being RG, that's not as relevant, just worth a note. If I wasn't PLing toons, this is the part where I would generally just DS PL to finish it off to whatever level was needed to group with end game at the time--**
75-100 - You can start doing CotF era Heroic Adventures at 75. Gribble (Dead Hills) and Marla (ETWK) have the easiest ones to start with. Expansion currency for everyone to replace gear.
Alternative - Gyrospire Zeka is a great grind zone into the 80's (get those anti-summoned nukes out again)
Then HoT zones/quests open up. HoT mission exp was nerfed at launch of VoA, but it's still pretty good. Sanctum Somnium center carpet is a great grinding spot around 90.
From here on I don't recommend alternate routes for lower/mid 90's to around 100. The HA's are probably the way to go.
Around 100-105 - TBM era HA's - Expansion currency for everyone to replace gear and buy up the first heroic stat inflation type 5 augs.
105-110 - Grinding EoK and RoS zones is likely the way to go. (Basically any EoK zone is viable but Frontier Mountain and RoS Sathir's Tomb are particularly popular)
110 -115 - The massive experience bonus for first time completion of ToV achievements is hard to beat and will take you the entire way.