Per my LATCH CEU from our statewide update on Aug 1, 2008: LATCH anchors must currently be tested to 65 lbs, and that will soon go to 100 lbs. This is why there is so mch goofiness about LATCH. It keeps getting ratched up, but by not calling each revision of LATCH something like LATCH 1.0, 2.0, 3.0, etc they are going by the lowest common denomenator. Ie... The original LATCH vehicles circa 1992. It's why some cars defer to the seat manufacturer, which allows car seat manufacturers to increase their LATCH weight limits at some time in the future, or they defer to the vehicle manufacturer which could mean the former, or could mean that your particular vehicle was never tested beyond the 40 lb weight limit. Yep. It's confusing as hell, which is counterintuitive to what LATCH was supposed to be about. Making installs and such easier on the parent/caregiver.
Would I top tether (not lower anchor) any FF seat or HBB booster, even if my child was over the "official" 40 lb weight limit for LATCH? You bet your bippy! Why? It's a lot safer due to sigificantly reduced head excursion, and I've been properly assured by people I trust that the top tethers have been tested to withstand that extra weight.
Try this link for more info:
http://www.saferidenews.com/html/LATCH_P49.htm