I agree that you can make a case about multipliers... they of course only happen once so a third level orc with 40 hits is 75+40+60 or 175 XP (x5 for the first one or 900 xp) and 350 for the second... but every other orc in the adventure is only 175 and once routine forever after it is only half value so the multipliers have diminishing returns.
OK, I see that we have quite different XP usage even with the old RM rules. A 3rd level orc would be worth far more XP in our group as we use the RMSS Kill Point rules, which are more akin to the RMC Kill Points Table 09-04. This gives 300 points for the 3rd level orc + 40 points for his 40 hits and this total of 340 points gets multiplied by 1.5 as the orc is an intelligent creature (the latter is AFAIK not a RMC rule, but only RMSS/RMFRP) resulting in ~500 XP, or 2500 XP for the first orc killed.
When you look at the example adventure in the back of RME it has an example XP rewards. So the scenario has two combats, and a few tasks that can be preformed for xp with a goal of rescuing someone... gives and example of that having up to 3500 xp without bonus awards by the GM.
It is hard to judge how many XPs a character would earn using the RMSS (and RMC, if options are used) XP system as it heavily depends on factors like criticals sustained, who kills how many monsters etc. My guessing would be that the PCs could each kill one Giant Ant in the adventure ((200 + 40)*5=1200 XP) and either an Orc or Goblin ((250+50)*1.5*5=2250). If the PCs are not harmed at all during the combats and succeed in no maneuvers they would only get on average an additional 50% Idea Points on top of the above XP for a total of (1200+2250)*1.5=5175 XPs. With perhaps a first C critical sustained and a few Spell Points and Maneuver Points they could get a bit more, maybe about 7000 XPs.
Nevertheless the example adventure in this comparison gives at least about half the XPs which I would have expected, which is at least a better ratio than I had in my example above (which was 1/4 to 1/3). The main reason is that the main adventure goal is rated as Very/Extremely Hard which gives quite a lot of XPs.
Really for just a few encounters to make up for 1/3 of a level is not a bad rate of advancement... but then again the GM ultimately sets the pace. For me the sample adventure would not be enough to level in any system I play in... it is just a one session adventure (I usually like 2 to three sessions between levels).
I admit that the RME XP system can fulfill this expectation, especially if GMs use similar rewards as in the example adventure. Perhaps I simply had the "wrong" expectation. I'd rather have expected to advance levels quite quickly during the first sessions, having the PCs advance a level rather twice in three sessions, with that rate going down later.
HARP for example sets first level at 350 points but this increases with each level until that reaches 2500 per level... which is HARP's quick acceleration xp system. RM stays at 10000 per level for quite a while.
Nevertheless, if you use a multiplier of around 30, you can easily convert from HARP levels to RM levels. Level 2 in HARP requires +350 XPs, in RM +10000 (x28.6), level 5 in HARP requires +1700 XPs, in RM +40000 (x23.5), level 10 in HARP requires +4950 XPs, in RM +140000 (x28.3), level 20 in HARP requires +15200 XPs, in RM +490000 (x32.2).
When I GM first level HARP... I am stingy, and no less than a half dozen encounters will make first level for me... I seldom give out more than 100 points for an encounter, because in HARP terms all combat is a minor party goal (saving your skin). I often give out role playing bonuses for HARP of up to 75 XP for good players (which is significant at low levels) each session.
Then it is strange that, using the same difficulty ratings as in the example adventure, a HARP character would get 100 XP for a Hard Minor Party Goal to fend of the Giant Ants + 100 XP for a Hard Minor Party Goal for avoiding the pit + 200 XP for a Hard Major Party Goal for solving the adventure, for a total of 400 XP i.e. straight into level 2. Why such a difference?
There is nothing to prevent more rapid advancement at low levels if the GM decides it is necessary.
I still wonder why the pace seems so different between the HARP and RME guidelines.