I went through the border at Cuatemoc MX/LaMesilla GT about 5 weeks ago, on the highway between San Cristobal and Quetzaltenango. Super easy, you can park your bike right in front of the offices, the bike is only out of your site for a couple minutes, so I wouldn't be too worried about having a buddy for the crossing.
I am in San Pedro on Lake Atitlan until Friday, if you want to stop here. Xela is worth spending some time in though, to adjust to the Guatemalan vibe. San Cristobal to Xela is doable in a day, including the border crossing.